# Hall sensor VIOUT voltage when current sensed = 1.5A

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#### kubeek

##### Well-Known Member
No, the output is I*0.4ohm+0.1*Vcc, which for I=1.5A and Vcc=5V is 1100mV.

#### ronsimpson

##### Well-Known Member
The 10AU version: Zero current = 1/10 supply.
0.4V/1A + (Vcc/10)
Range 0 to 10A.

The 5AB version: 0.4V/1A with and offset of 1/2 supply. Zero current = 1/2 Vcc. Range=_5 to +5A

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#### alec_t

##### Well-Known Member
Bear in mind too that, as those specs show, the "Vcc x 0.5" is only a typical value, with no min or max given. So the output will need to be calibrated.

#### Flyback

##### Well-Known Member
sorry but for the unidirectional one of the top post, the "0.1 x vcc" that gets outputted for zero current is just due to the output opamp not being able to take its output down to 0v........the "0.1 x vcc" is not stated as being an offset, so for a sensed current of 1.5A, the output would be just 0.6V, surely?

In the bidirectional case, with a single supply, the output does need to have the permanent 2.5V offset so that you can distinguish between current flowing in either direction, so that is surely a different case.

The datasheet on page 8 states that the actual offset voltage is only 15mV. -Noting that it is not calling the "0,.1 x vcc" an 'offset'...because it does not come into play when the sensed current is above 1.25A, surely?

#### kubeek

##### Well-Known Member
No, if for any current between 0A and 1.25A the output stayed at 0.5V and then went from 0.5 to 0.6V between 1.25 and 1.5A the thing would be a very lousy and useless device. The offset is there precisely to get around the limitations in the opamp, not an effect of saturation and bad design.
Page 8 says offset is 0.1*Vcc, and accuracy on top of that is +/-15mV.
See page 18 for explanation of their terminology, however I am sure you have already read that

#### Flyback

##### Well-Known Member
Thanks but page 8 doesnt call "0.1 x vcc" an "offset"...it just says its the zero current output voltage....and it is surely simply the fact that the opamp cannot give an output at its low rail.
It doesnt make it a lousy device......for our application, it is perfectly fine that it gives 500mV for 0 to 1.25A, and then gives 400mV/A for 1.25A and greater.

#### kubeek

##### Well-Known Member
....and it is surely simply the fact that the opamp cannot give an output at its low rail.
I bet you that it is not. Get a sample and measure it if you can´t comprehend the datasheet.

Can you explain to me why would anyone want to produce such a crippled device? It makes no sense what so ever. No one will buy a device that starts working above 1.25A, and you are a one in a million case where such a behavior is useful.

And what about the bipolar devices? Do you think the 0.5*Vcc zero current output is also a manifestation of a screwed opamp, i.e any current from minus inifity to plus 6.25A is thrown away and anything above 6.25A starts showing on the output? Come on, you can´t be serious...

#### alec_t

##### Well-Known Member
I agree with Kubeek, post #2. As per the datasheet for the unidirectional IC the output voltage just ramps up linearly at 400mV/A from a starting point of 0.1 x Vcc.

#### eTech

##### Well-Known Member
VIOUT is about 1100mv. After removal of offset, its about 600mv (shifted output on graph).
I also get the same measurements on the bench.
See attached.

BTW- LTspice XVII has been released.

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#### Flyback

##### Well-Known Member
Thanks, it would be nice to see what you get when you ramp the current from 0 to 1.5.
I looked for a spice model of it but couldnt find it.

#### eTech

##### Well-Known Member
Thanks, it would be nice to see what you get when you ramp the current from 0 to 1.5.
I looked for a spice model of it but couldnt find it.
Hi.

Attached is a simulated DC sweep from 1mA to 1500mA.
I'm also attaching a zip file containing the ACS723 series sensor models and a test circuit.
These are behavioral models I made for LTspice (Allegro didn't have them).
For the sim, I used the LTspice bundled universalopamp2 but for the bench I used an LM358.
I got very close results on the bench as I did on the sim.

BTW...I didn't model the BW pin, temperature, or magnetic coupling characteristics.

Have fun.

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#### Flyback

##### Well-Known Member
thanks, oh right, i thought you were simulating the ACS723 module provided by Allegro...so the one youre simulating is one you made for yourself, to behave as you believe it should behave?

#### eTech

##### Well-Known Member
thanks, oh right, i thought you were simulating the ACS723 module provided by Allegro...so the one youre simulating is one you made for yourself, to behave as you believe it should behave?
Yes.

I tried to get an evaluation board from allegro but they don't have them yet..

#### ronsimpson

##### Well-Known Member
so the one youre simulating is one you made for yourself, to behave as you believe it should behave?
I have learned much by:
2) Making the spice model
3) Turning on the real part and seeing how it works
5) Re-making the model
6) go step 3 (loop 10 times)

This is much like theology.
If you think things work (like this) it is easy to get the data sheet to agree with you.
A second person thinks things work differently and the data sheet agrees with them.
Likely neither is right.

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